diff --git a/src/groovy/uk/co/desirableobjects/sendgrid/SendGridEmail.groovy b/src/groovy/uk/co/desirableobjects/sendgrid/SendGridEmail.groovy
index 9a56c4c..125dd9c 100644
--- a/src/groovy/uk/co/desirableobjects/sendgrid/SendGridEmail.groovy
+++ b/src/groovy/uk/co/desirableobjects/sendgrid/SendGridEmail.groovy
@@ -65,8 +65,8 @@ class SendGridEmail {
 
         Map<String, Object> parameters = [:]
 
-        attachments.each { String filename, File attachment ->
-            parameters.put("files[${filename}]" as String, attachment.bytes)
+        attachments.each { String filename, attachment ->
+            parameters.put("files[${filename}]" as String,  attachment instanceof byte[] ? attachment: attachment.bytes )
         }
 
         return parameters
diff --git a/src/groovy/uk/co/desirableobjects/sendgrid/SendGridEmailBuilder.groovy b/src/groovy/uk/co/desirableobjects/sendgrid/SendGridEmailBuilder.groovy
index eeef75b..72042c9 100644
--- a/src/groovy/uk/co/desirableobjects/sendgrid/SendGridEmailBuilder.groovy
+++ b/src/groovy/uk/co/desirableobjects/sendgrid/SendGridEmailBuilder.groovy
@@ -68,7 +68,7 @@ class SendGridEmailBuilder {
         return this
     }
 
-    SendGridEmailBuilder addAttachment(String filename, File file) {
+    SendGridEmailBuilder addAttachment(String filename, file) {
 
         if (filename.contains('[') || filename.contains(']')) {
             throw new IllegalArgumentException('You cannot use square brackets in attachment filenames')